In recent years, in automobiles, various information is required on such as the load acting on wheels and the rotational speed of the wheels in order to affect driving control at the time of traveling. To obtain such information, a proposal has been made to provide a sensor device to a rolling bearing device for a wheel to which the wheel of an automobile is mounted.
The eccentricity of the tire as an example of information concerning the state of the wheel during traveling is brought about by such as a faulty wheel balance, a decrease of tire air pressure, and an unbalanced weight of the tire (e.g., a case where a stone is sandwiched between dual tires of a large-sized vehicle). If the automobile is caused to travel with an eccentric tire, vibrations can be generated to aggravate the riding comfort, and traveling stability can be impaired. In some cases, there is a possibility of the tire undergoing a fatigue to result in a burst.
Accordingly, various techniques for detecting an abnormality of the tire including such eccentric have hitherto been proposed. For example, patent document 1 discloses a device for detecting an abnormality of the tire by disposing in the tire a sensor for detecting the force transmitted from the tire. In addition, patent document 2 discloses a system wherein the tire inflation pressure, the temperature of a belt edge, and the like are measured, and collation is made with a damaged model prepared in advance as a map to thereby affect the monitoring or diagnosis of the vehicle tire.
Meanwhile, as such a sensor device for detecting the load acting on the wheel, a sensor device has been proposed which consists of a magnetic impedance sensor provided on, for instance, the fixed bearing ring and a magnetized portion provided in face-to-face relation to that magnetic impedance sensor (e.g., patent document 3). In this sensor device, however, since the detection by the magnetic impedance sensor is affected by such as the material and the shape of a portion to be detected, there have been problems in that there is a restriction in the selection of the material of the rolling bearing, and that the processing of the magnetized portion and the addition of another member are required for the portion to be detected.
Accordingly, as a rolling bearing device with a sensor in which such a restriction in material selection is small and additional processing is made unnecessary, a rolling bearing device with a sensor has been proposed in which ultrasonic sensors are disposed on the fixed bearing ring to thereby detect the force acting between the rolling element and the fixed bearing ring as echo ratios (e.g., patent document 4).
The rolling bearing device with a sensor disclosed in this patent document 4 has a sensor device which is comprised of ultrasonic sensors which are provided at least two positions spaced apart a predetermined interval in the circumferential direction of a fixed-side bearing member and adapted to detect the rolling element load as an echo ratio, as well as a processor for determining from outputs of the ultrasonic sensors at least a component in a vertical direction and a component in a left-right direction among three-direction components of the load acting on the rolling bearing. Additionally, it is stated therein that it is also possible to determine not only the three-direction components but also moments about an X-axis, a Y-axis, and a Z-axis.    [Patent Document 1] JP-2000-203217A    [Patent Document 2] Published Japanese translation of a PCT application JP 2005-528270T    [Patent Document 3] JP-2004-45370A    [Patent Document 1] JP-2006-177932A